1. Field of the Invention
This invention relates in general to multitrack magnetic heads and to methods and parts for forming such heads.
2. Description Relative to the Prior Art
In the art of magnetic recording, there is a trend toward the use of multitrack magnetic heads having large numbers of cores per unit width across the head surface that interacts with the recording medium. One explanation for this trend may be found in the fact that a plurality of head cores can record a specific amount of data at an information writing speed which is only about ##EQU1## of the information writing speed which would be required when writing with only one core. For example, for a playback gap length of, say 100.mu." (.mu."=microinch), a bandwidth of 2 MHz would necessitate a single core writing speed of 200 inches per second (ips) if use of the recording medium is to be optimized. By contrast (still using playback gap lengths of 100.mu."), that same bandwidth of 2 MHz can be written by a 500-track record head at a relative head-to-medium speed of only 0.4 ips ##EQU2## Such recording of a large bandwidth in a large number of tracks at low writing speed suggests, among other things, the linear tape recording of video information. Linear tape recording of video information, as opposed to the recording techniques employed in helical scan and quadruplex video recorders, implies a simplification of hardware: not only does a lessened information writing speed relax the mechanical demands of the recording operation, but head switching, rotary head drums, and various electronics are obviated, as well.
With the above as background, consider for a moment a multitrack magnetic record head comprised of a stack of head cores with their respective gaps aligned along a gap line; and imagine, for example, a common signal-carrying coil linking all such cores. By sucessively turning ON, and OFF, each core in the stack by means of a respective ancillary control, each core will take a time-division sample of the signal in the common coil . . . and if the line of core gaps is in contact with a recording medium (magnetic tape), a plurality of time-division samples will be recorded in respective tracks of the medium. Such a scanning magnetic head has been the vision of those in the video recording field for some time, whereby the whole concept of linear video recording would become commercially practicable. By time-division sampling of, say, an NTSC video signal, each picture element of each line could be recorded in a respective track at a low relative head-to-tape speed. In a similar way, playback of such a multitrack recording could be effected by successively switching ON, and OFF, the cores in the stack, thereby to induce, successively, corresponding element signals in the common coil which links the cores.
Various techniques are known for selectively, and individually, switching head cores ON and OFF: See, for example, U.S. Pat. application Ser. No. 133,076, now U.S. Pat. No. 4,346,417 and U.S. Pat. application Ser. No. 127,278, now U.S. Pat. No. 4,322,763.
Turning, for the moment, from the matter of the aforenoted use of a scanning magnetic head, it will be appreciated that certain processes for the fabrication of head parts, and components useful therewith, are susceptible to batch-fabrication techniques. U.S. Pat. No. 4,158,213, for example, teaches the use of deposited thin magnetic films on nonmagnetic substrates as one vehicle for use in the manufacture of many multitrack magnetic heads at one time. Similarly, the relatively recent commercial introduction of integrated circuits, including such structures as charge-coupled devices (CCDs), which utilize metal-oxide-semiconductor (MOS) technology, was brought about, to a great extent, by the cost-saving batch-processing of semiconductor silicon wafers having selectively gaseously doped diffusions, and photolithographically produced metallic electrodes.